Chapter 7 - Bone Tissue

Question 0

What are bones?

Answer 0

Connective tissue in which the matrix is hardened by the deposition of calcium phosphate and other minerals

Question 1

What are the functions of the skeleton?

Answer 1

1. Support - bones hold up the body and provide support for muscles.
2. Protection - bones enclose and protect vital organs.
3. Movement - produced by the action of muscles on the bones.
4. Electrolyte balance - the skeleton stores calcium and phosphate ions and releases them into the tissue fluid and blood as needed.
5. Acid-base balance - bone tissue buffers the blood against excessive pH changes by absorbing or releasing alkaline phosphate and carbonate salts.
6. Blood formation - red bone marrow is the major producer of blood cells.

Question 2

What is Osseous tissue?

Answer 2

Contains blood, bone marrow, cartilage, adipose, neurons, and fibrous CT

Question 3

What are the categories of bones?

Answer 3

a) Flat bones - thin curved plates.
b) Long bones - serve as rigid levers that are acted upon by skeletal muscles to produce movement.
c) Short bones - bones equal in length and width that produce limited gliding movements.
d) Irregular bones - bones that don’t fit any other category.

Question 4

What is the general anatomy of long bones?

Answer 4

a) Compact bone -
b) Marrow cavity - space enclosed by compact bone which contains bone marrow.
c) Spongy bone - loosely organized bone tissue filling the central space of the ends of the bone, and the middle of non-long bones.

Question 5

What are the features of long bones?

Answer 5

a) Diaphysis - the shaft that provides leverage.
b) Epiphysis - the head at each end of the bone that strengthens the joint and provides added surface area for attachment.
c) Articular cartilage - a layer of hyaline cartilage that covers the joint surface where one bone meets another.

Question 6

What are the linings of the bone?

Answer 6

a) Periosteum - an outer layer of collagen and inner layer of bone-forming cells.
b) Some of the collagen fibers are continuous with tendons binding muscle to bone.
c) Endosteum - layer of CT that lines the marrow cavity, covers the surfaces of spongy bone and lines the canal system.
d) Epiphyseal plate - hyaline cartilage in children separating the marrow spaces of the epiphysis and diaphysis, a zone where bones grow in length.

Question 7

What is the anatomy of flat bone?

Answer 7

a) Two layers of compact bone enclosing a middle of spongy bone.
b) The spongy bone may absorb impact of a blow to the cranium (head) even if the outer compact bone is fractured.

Question 8

What are the bone cells?

Answer 8

1. Osteogenic cells - stem cells in the endosteum and periosteum that multiply continually and give rise to osteoblasts.
2. Osteoblasts - bone-forming cells that synthesize the organic matter of the bone matrix, which is hardened they deposited.
3. Osteoclasts - bone-dissolving cells found on the bone surface.

Question 9

What is the Matrix?

Answer 9

1. The matrix by dry weight is 1/3 organic and 2/3 inorganic matter.
2. The organic matter includes collagen and other molecules.
3. The inorganic matter 85% hydroxyapatite, a calcium phosphate salt and 10% calcium carbonate with lesser amounts of other matter.
4. Bone is a composite of collagen giving flexibility with tensile strength and hydroxyapatite giving the strength to support the weight of the body.

Question 10

What is an Osteon?

Answer 10

Cylinder of tissue surrounding a central canal

Question 11

What is concentric lamellae?

Answer 11

Rings of matrix

Question 12

What is the central canal?

Answer 12

Passage way containing nerve, artery, and vein

Question 13

What are perforating canals?

Answer 13

Passage ways that join central canals

Question 14

Compact Bone Histology

Answer 14

1. Osteon - cylinder of tissue surrounding a central canal.
2. Blood vessels enter the bone tissue through nutrient foramina on the surface which opens into the perforating canals.
3. The innermost osteocytes receive nutrients from the BV and pass them along through gap junctions and canaliculi to neighbors.

Question 15

What is the histology of spongy bone?

Answer 15

1. The bone consists of a lattice of bone called spicules and trabeculae.
2. Lamellae but no central canals because no osteocyte is far from marrow.
3. Spongy bone imparts strength to a bone while adding minimum weight.
4. The trabeculae are arranged along the bones lines of stress.

Question 16

What is the histology of bone marrow?

Answer 16

1. Bone marrow is the soft tissue that occupies the marrow cavity and the spaces in the spongy bone.
2. Red marrow- tissue that produces blood cells in the marrow cavities of children and the spongy bones of the skull, vertebrae, sternum, hips, and heads of long bone.
3. Yellow marrow - fatty tissue in marrow cavities of most adult bones.

Question 17

What is intramembranous ossification?

Answer 17

It produces the flat bones of the skull and most of the clavicle.

Question 18

What are the stages of intramembranous ossification?

Answer 18

a. Mesenchyme condenses into a layer of soft tissue permeated by blood capillaries and becomes trabeculae.
b. Osteoblasts deposit a matrix of collagen, minerals deposit on the matrix, and the cells are trapped becoming osteocytes.
c. Osteoblasts continue to deposit collagen and the bony trabeculae creates spongy bone.
d. Trabeculae at the surface continue to calcify until the spaces are filled, converting the spongy bone to compact bone.

Question 19

What is endochondral ossification?

Answer 19

1. Bone is preceded by a hyaline cartilage “model”, most bones develop this way.
2. Adult bone has a single marrow cavity and the epiphyseal plate is closed (epiphyseal line). The bone can no longer grow in length.

Question 20

What are the stages of endochondral ossification?

Answer 20

a. Mesenchyme develops into a hyaline cartilage model covered by a perichondrium.
b. Perichondrium begins producing osteoblasts, which deposit a bony collar around the middle.
c. Meanwhile, chondrocytes in the middle enlarge forming the primary ossification center (POC).
d. The matrix calcifies blocking nutrients to the chondrocytes.
e. The chondrocytes die and the lacunae merge into a single cavity.
f. BV invade the cavity.
g. The cavity fills with stem cells and blood and becomes the primary marrow cavity.
h. Meanwhile, osteoblasts enter the cavity and deposit tissue which calcifies to form bony trabeculae.
i. Calcification of cartilage continues toward the ends of the bone and chondrocytes enlarge at the ends of the bone.
j. Chondrocytes enlarge at the end of the bone forming secondary ossification centers.
k. Secondary ossification centers hollow out by the same process to form secondary marrow cavities at the epiphyses.
l. The epiphysis fills with spongy bone, cartilage is limited to the articular cartilage and the epiphyseal plate.

Question 21

What is the histology of bone elongation?

Answer 21

1. The epiphyseal plate is a region of transition from cartilage to bone and functions as a growth zone where the bone elongates.
2. Metaphysis - the transitional zone, facing the marrow cavity.
3. Osteoblasts deposit layer after layer of bone matrix converting spongy bone to compact bone.
4. Growth in height occurs as the end zone of reserve cartilage is continually pushed toward the ends of the bone.
5. Anchondroplastic dwarfism results from failure of cartilage growth in the long bone.

Question 22

What are the zones of metaphysis?

Answer 22

a. Zone of the reserve cartilage - resting cartilage.
b. Zone of cell proliferation - chondrocytes multiplying.
c. Zone of cell hypertrophy - chondrocytes enlarge.
d. Zone of calcification - mineral deposition calcifies cartilage matrix.
e. Zone of bone deposition - chondrocytes die, osteoblasts invade and deposit bone thus forming trabeculae.

Question 23

What is the histology of bone widening and thickening?

Answer 23

1. Bones grow in diameter and thickness throughout life.

2. Appositional growth - deposition of new tissue at the surface.

Question 24

What happens during apposition all growth?

Answer 24

a. Osteoblasts of the periosteum deposit tissue on the bone surface, the tissue calcifies and the osteoblasts become trapped.
b. Osteoclasts of the endosteum dissolve tissue on the inner bone surface widening the marrow cavity.

Question 25

What is the histology of bone remodeling?

Answer 25

1. Bones are continually remodeled with absorption of old bone by osteoclasts and deposition of new bone by new osteoblasts.
2. Wolff’s law of bone - architecture of a bone is determined by mechanical stresses placed upon it, the bone adapts to withstand those stresses.
3. If a bone is heavily used or a stress is consistently applied, osteoblasts deposit new tissue and thicken the bone.

Question 26

What is the physiology of osseous tissue?

Answer 26

A: 1. Mineral deposition - a process in which calcium, phosphate, etc. are taken from the blood plasma and deposited in bone tissue.
A: 2. Mineral resorption - a process of dissolving bone.
B. Calcium homeostasis.
C. Hormones that balance calcium.
D. Phosphate homeostasis.
E. Other factors affecting bone.

Question 27

What is the physiology of mineral deposition?

Answer 27

a. Osteoblasts lay down collagen fibers which become encrusted with hydroxyapatite crystals that harden the matrix.
b. Most tissues have inhibitors to prevent calcification, but osteoblasts neutralize the inhibitors in bone.
c. Ectopic ossification - abnormal calcification of tissue.

Question 28

What is the physiology of mineral resorption?

Answer 28

a. Resorption is carried out by osteoclasts and releases minerals into the blood.
b. Osteoclasts have receptors for calcium and respond to falling levels of calcium in the tissue fluid.
c. Osteoclasts secrete H+ and Cl- follows forming HCl which dissolves the minerals and secrete acid phosphatase that digest collagen.

Question 29

What is the physiology of calcium homeostasis?

Answer 29

1. Calcium plays roles in communication among neurons, muscle contraction, blood clotting, and exocytosis.
2. Phosphate groups are also components of DNA, RNA, ATP, phospholipids and other compounds.
3. The skeleton is a reservoir in which these minerals are deposited and withdrawn.

Question 30

What changes in blood calcium concentration can have serious consequences?

Answer 30

a. Hypocalcemia (deficiency) causes excessive excitability of the nervous system and leads to muscle tremors, spasms, or tetany.
b. Hypercalcemia (excess) - nerve muscle cells are less excitable causing depression of the nervous system, muscle weaknesses, sluggish reflexes and cardiac arrest.

Question 31

What are the hormones that balance calcium?

Answer 31

1. Calcitriol
2. Calcitonin
3. Parathyroid hormone

Question 32

What does calcitriol do?

Answer 32

a. Using UV radiation the keratinocytes in the skin synthesize an inactive form of vitamin D which is converted to the active form.
b. It raises blood Ca2+ levels by increasing small intestine absorption, bone resorption and kidney reabsorption of calcium.
c. It ensures the Ca2+ and phosphate levels in the blood are adequate for deposition.

Question 33

What does calcitonin do?

Answer 33

a. Secreted from thyroid gland when blood calcium is too high.
b. It lowers blood calcium levels by inhibiting osteoclast activity.
c. Important in children, but has a weak effect in adults.

Question 34

What does the parathyroid hormone (PTH) do?

Answer 34

a. Secreted from the parathyroid glands when blood calcium is low.
b. It raises blood Ca2+ levels by increasing bone resorption and kidney reabsorption, enhancing effects of calcitriol, and inhibiting bone deposition.

Question 35

What us the physiology of phosphate homeostasis?

Answer 35

1. Phosphate levels are not regulated as tightly as calcium.

2. Changes in plasma phosphate level are not associated with any disorder.

Question 36

What are the other factors that affect the bone?

Answer 36

1. At least 20 hormones, growth factors, and vitamins affect bone tissue.
2. Bone growth is especially rapid in puberty when surges in growth hormone, estrogen, and testosterone promote ossification.
3. Sex steroids eventually deplete the cartilage of the epiphyseal plates and bring closure of the epiphysis.
4. Use of steroids by adolescent can cause premature closure and result in abnormally short adult stature.

Question 37

What are the different types of fractures?

Answer 37

1. Stress fracture - a break caused by abnormal trauma to a bone.
2. Pathological fracture - a break in a bone weakened by some other disease.

Question 38

What are the types of healing of fractures?

Answer 38

a. Hematoma formation - bleeding in the bone causes a clot to form.
b. Granulation of tissue - the clot is converted to granulation tissue by invasion of cells and blood capillaries.
c. Soft callus formation - fibroblasts deposit collagen in the granulation tissue and chondroblasts produce fibrocartilage.
d. Hard callus formation - osteoblasts deposit a bony collar around the fracture to unite the broken pieces.
e. Bone remodeling - osteoclasts remove fragments of bone while osteoblasts deposit spongy bone then convert it to compact bone.

Question 39

What are the types of repair?

Answer 39

1. Closed reduction - a procedure in which bone fragments are manipulated into their normal positions without surgery.
2. Open reduction - surgical exposure of the bone and the use of plates, screws, or pins to realign the fragments.

Question 40

What are other types of bone disorders?

Answer 40

1. Rickets - soft bones in children from vitamin D deficiency.
2. Osteomalacia - soft bones in adults from vitamin D deficiency.
3. Osteitis deformans (Paget’s disease) - excessive proliferation of osteoclasts with bone resorption and osteoblasts attempt to compensate by depositing extra bone.
4. Osteomyelitis - inflammation of bone tissue and bone marrow as a bacterial infection.
5. Osteogenesis imperfecta - a defect in collagen deposition that renders bones exceptionally brittle.
6. Osteosarcoma - bone cancer most often in the tibia, femur, and humerus of males between 10 and 25.
7. Osteoporosis - severe loss of bone density resulting in brittle bones with increase of fractures especially in the hip, wrist, and vertebra.